A dump truck is generally provided with a frame having four wheels disposed thereon. Above a front section of the frame, an operator's cab and control box are arranged. On the frame, a body is mounted extending over the frame from a middle to a rear of the frame.
Via hinge pins attached to a rear of the frame and hoist cylinders attached on the frame at locations forward of the hinge pins, the body is connected to the frame. In association with an extension or contraction of the hoist cylinders, the body pivots in an upward or downward direction (rises or lowers) about the hinge pins.
On the body of the dump truck, an object to be hauled, such as earth, sand or crushed stone, is loaded in a heap, for example, by a hydraulic excavator or the like. The dump truck is constructed such that by changing the body from a lowered position to a raised position, the object loaded on the body can be unloaded (see, for example, Patent Citations 1 and 2).
The body is provided with a payload section formed by a floor board forming a floor, a front board located on a front side of the floor board and forming a front wall, and a pair of side boards located on opposite sides of the floor board. To an upper part of the front board of the body, a canopy is connected extending forward such that the canopy covers the operator's cab and control box.
Attached to a lower surface of the floor board of the body is a pair of rails, which are arranged extending in a longitudinal direction of the frame. Each rail is a hollow box-shaped structure member comprised of two side rail plates and a bottom rail plate. The two side rail plates extend downwardly from the floor board of the body, and the bottom rail plate is in contact with respective lower end surfaces of the two side rail plates. It is to be noted that the bottom rail plate is often provided with rubber pads as cushioning members. These rubber pads serve to prevent vibrations of the body during traveling, and also to absorb impacts to the frame upon loading earth or sand on the body.
On the lower surface of the floor board of the body, a plurality of laterally-extending stiffeners (reinforcing members) are also attached at intervals in the longitudinal direction such that these plural stiffeners intersect with the paired rails. It is to be noted that each stiffener is a structure member comprised of a channel steel. The floor board, front board, paired side boards, canopy, the paired rails and individual stiffeners of the body have been joined together by welding. The rigidity of the floor board of the body is assured by the paired rails and the plural stiffeners.
When an object to be hauled is loaded in a heap in the payload section of the body, a high load is applied to the body from the object to be hauled. The load applied to the body is received via the floor board of the body at parts connected to the rails and parts connected to the hinge pins, specifically hinge brackets. The load applied to the rails is borne by the frame which supports the rails. On the other hand, the load applied to the hinge brackets of the body is borne by the frame via the hinge pins.
Upon raising the body to unload the hauled object, a high load is applied to the hinge brackets, and therefore, relatively thick plates are used for the hinge brackets to assure high rigidity for them. On the other hand, the rails are arranged on the lower surface of the floor board of the body over a wide range extending in the longitudinal direction, and therefore, relatively thin plates are assembled into box structures to assure rigidity for the rails.